[jira] [Created] (SPARK-23334) Fix pandas_udf with return type StringType() to handle str type properly in Python 2.

["Takuya Ueshin (JIRA)" <ji...@apache.org>]

Takuya Ueshin created SPARK-23334:
-------------------------------------

             Summary: Fix pandas_udf with return type StringType() to handle str type properly in Python 2.
                 Key: SPARK-23334
                 URL: https://issues.apache.org/jira/browse/SPARK-23334
             Project: Spark
          Issue Type: Bug
          Components: PySpark, SQL
    Affects Versions: 2.3.0
            Reporter: Takuya Ueshin


In Python 2, when pandas_udf tries to return string type value created in the udf with {{".."}}, the execution fails. E.g.,

{code:java}
from pyspark.sql.functions import pandas_udf, col
import pandas as pd

df = spark.range(10)
str_f = pandas_udf(lambda x: pd.Series(["%s" % i for i in x]), "string")
df.select(str_f(col('id'))).show()
{code}

raises the following exception:

{code}
...

java.lang.AssertionError: assertion failed: Invalid schema from pandas_udf: expected StringType, got BinaryType
	at scala.Predef$.assert(Predef.scala:170)
	at org.apache.spark.sql.execution.python.ArrowEvalPythonExec$$anon$2.<init>(ArrowEvalPythonExec.scala:93)

...
{code}

Seems like pyarrow ignores {{type}} parameter for {{pa.Array.from_pandas()}} and consider it as binary type when the type is string type and the string values are {{str}} instead of {{unicode}} in Python 2.



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